Characterization of growth hormone nycthemeral plasma profiles in catheterized rainbow trout (Oncorhynchus mykiss)

Abstract

This study was conducted in order to characterize the nycthemeral plasma profiles of growth hormone (GH) in 41 prepubertal (2+) rainbow trout (Oncorhynchus mykiss). The possible influences of day‐night alternation and of the food factor (quantity ingested, timing of the feed) on these plasma profiles were also analysed. Blood samples were taken every hour during a 24‐hour period through a catheter inserted in the dorsal aorta. An assay of cortisol levels showed that the fish were in satisfactory physiological condition. The plasma concentrations of GH fluctuated significantly during the course of a nycthemere. The basal level was very low (0.32 ± 0.01 ng/ml), and was interrupted by peaks that occurred at a rate of 2.1 ± 0.1 peaks/24 hr, an amplitude of 2.0 ± 0.3 ng/ml, and a duration of 3.5 ± 0.2 hr. As a result, mean GH levels over a 24‐hr period were low (0.7 ± 0.1 ng/ml). Peaks occurred irregularly and asynchronously in individual fish and displayed no rhythmicity. Our study shows that there is a sexual difference in GH profiles in rainbow trout. No significant difference was observed between daily and nightly levels of GH (0.6 ± 0.07 vs. 0.8 ± 0.1 ng/ml). No influence of the diet on the plasma profiles of GH was observed. Average levels of GH over a 24 hr period are not significantly correlated with the growth rate of the fish. This study shows that circulating levels of GH in rainbow trout are markedly lower than in other vertebrates. © 1996 Wiley‐Liss, Inc.

Daily variations of the saccular endolymph and plasma compositions in the turbot Psetta maxima:relationship with the diurnal rhythm in otolith formation

“…This could explain the magnitude of the standard errors due to individual variability. Nycthemeral variations of cortisol have been reported in freshwater fish by Pickering & Pottinger (1983) and Gomez et al (1996), who concluded that cortisol increases are intrinsic phenomena not caused by stress. To our knowledge similar studies have not been made with seawater fish.…”

Variability in the characteristics of ultradian and circadian rhythms in plasma levels of growth hormone in the Indian walking catfish,Clarias batrachus

“…Niu et al (1993) recorded the pulsatile pattern of GH secretion in rainbow trout. However, Gomez et al (1996) did not record any significant rhythm in GH secretion, yet the plasma level of GH fluctuated over the day-night cycle, although peaks occurred irregularly and asynchronously in individual rainbow trout. Reddy and Leatherland (1995) have reported significant postprandial peaks in plasma GH in rainbow trout that phase shifted with time of feeding.…”

“…They recorded either one episode (single or several pulses clustered) or two episodes with a 2.6-h interval. A diurnal variation in GH secretion in rainbow trout has also been demonstrated, but data are highly variable (Gomez et al 1996). Le Bail et al (1991) have reported daily fluctuations in plasma GH in both sexes of Chinook salmon with individual variations with regard to frequency and timing of GH peaks.…”

“…A good number of reports are available on the rhythmic secretory pattern of gonadotropin (de Vlaming and Vodicnik 1977;Hontela and Peter 1978;Khan and Thomas 1994;Harikrishanan et al 2002), sex steroids (Lamba et al 1983;Singh and Singh 1987) and thyroid hormones (Stacey et al 1984;Cook and Eales 1987;Sinha et al 1992). Plasma levels of GH are also reported to undergo seasonal and diurnal variation in fishes (Marchant and Peter 1986;Le Bail et al 1991;Bjornsson et al 1994;Zhang et al 1994;Gomez et al 1996;Bjornsson et al 2002;Einarsdottir et al 2002;Mingarro et al 2002;Canosa and Peter 2005), but the results are highly inconclusive and debatable. Most of these studies on daily variation in GH have been performed only in a single month or on a single phase of the reproductive cycle.…”

Réponse au stress induit par le transport chez la truite arc-en-ciel (Oncorhynchus mykiss)

“…Les niveaux de Cortisol élevés observés chez les poissons du lot péché au petit jour, juste avant le transport, sont de l'ordre des valeurs maximales rapportées par GOMEZ et al (1996), pendant la nuit, chez des truites arc-en-ciel équipées d'un cathéter pour la prise de sang. Ces niveaux pourraient donc refléter aussi bien des variations naturelles qu'un premier stress lié à la pêche.…”